The present invention relates to the field of temperature sensing, and, more particularly, to temperature sensing for combustion turbine power generators.
An electrical power generator converts mechanical energy into electrical energy. A typical electrical power generator includes a stator and a rotor that rotates within the stator to thereby generate electricity. The rotor, in turn, is mounted to a shaft that drives the rotor. Various mechanical devices may be used to drive the shaft, such as a combustion turbine.
In a conventional configuration, the combustion turbine comprises a compressor to draw in and compress a gas (usually air), a combustor or heat source that adds energy to the compressed gas, and a turbine to extract power from a resulting heated gas expansion. In an electrical generator, the extracted power is used to drive the shaft, which, as already noted, rotates the rotor within the stator to thereby generate electricity.
The capacity of the combustion turbine may be increased if air drawn in by the compressor has a lower temperature relative to that which it will attain during combustion to drive the turbine. Accordingly, cooling the ambient air (typically referred to as inlet air) before it is drawn into the combustion turbine can be a cost effective way to increase the capacity of the combustion turbine. One approach to cooling the inlet air is with a direct refrigeration-cooling system in which ambient air is cooled using conventional refrigeration devices and techniques.
One drawback to refrigeration-cooling is parasitic power loss. This is due to the relatively large power drain needed to power a refrigerator unit. According to some estimates, the parasitic power loss can be as much as thirty percent (30%) of the increased power output of the turbine power generator.
An alternative inlet air cooling technique is provided by an evaporative cooling or fogging system. With such a system, moisture in the form of a water mist or spray is added to the inlet air. As the water evaporates, the temperature of the inlet air (the dry bulb temperature) is lowered to a new temperature (the wet bulb temperature), thereby cooling the inlet air before it is drawn into the compressor of the combustion turbine. An evaporative cooling system tends to be less expensive to install and to operate as compared with other techniques and devices.
Despite the advantages of evaporative cooling, measuring inlet air temperature may be made more difficult by an evaporative cooling system. Air inlet temperature typically has been measured in conventional combustion turbine power generators that lack an evaporative cooling system by using various temperature-sensing devices, including thermistors and thermocouples. As disclosed, for example, in U.S. Pat. No. 5,252,860 to McCartney et al. and U.S. Pat. No. 5,103,629 to Mumford et al., air temperature can be measured using a thermocouple positioned adjacent a compressor air inlet.
Similar such temperature sensing devices have also been employed with combustion turbine power generators that do use evaporative cooling. U.S. Pat. No. 5,930,990 to Zachary et al., for example, discloses an apparatus for adding nebulized water to a gas turbine. The water is added from a spray rack assembly comprising at least one water pipe and at least one corresponding water nozzle. The water is added through a duct that helps direct the water to a compressor inlet. Inlet air temperature is measured with a temperature sensor that, as illustrated, extends into the air flow path to which nebulized water has been added.
A problem associated with conventional temperature sensing devices when used in combustion turbine power generators that use evaporative cooling is that temperature readings may be adversely affected. Specifically, it may be observed that water droplets tend to form on an exposed temperature sensing device when nebulized water is added to the inlet air. When water droplets are carried by the inlet air and deposited on the temperature sensing device, the device may render an inaccurate reading owing to the tendency for the water to evaporate (as when borne by the inlet air) and thereby lower the temperature of the temperature sensing device.
This tendency is especially problematic in combustion turbine power generators using evaporative cooling since the amount of nebulized water that should be added is a function of the temperature of the inlet air. Misreading that temperature can result in an inappropriate amount of water mist being added to the inlet air.
It is therefore an object of the present invention to provide a device for more accurate, more reliable temperature sensing of the inlet air flow of a combustion turbine, especially one using evaporative cooling.
This and other objects, features, and advantages in accordance with the present invention are provided by an inlet air flow temperature sensor that includes a hollow body connected in fluid communication with an inlet air flow and having interior portions to define a tortuous path of air flow therethrough. A temperature sensing device may be carried by the hollow body. The tortuous path defined by the interior portions of the hollow body may reduce water accumulation on the temperature sensing device. With the inlet air flow temperature sensor, therefore, a more reliable and more accurate reading of a temperature of the inlet air flow may be obtained.
The inlet air flow temperature sensor may advantageously be used with a power generator apparatus that includes an electrical power generator, a combustion turbine, and an evaporative water cooler. The combustion turbine may drive the electrical generator and may have a combustion turbine inlet to receive an inlet air flow. The evaporative water cooler may evaporate water into the inlet air flow to cool the inlet air flow. Accordingly, the inlet air flow temperature sensor may be used to more accurately and reliably read temperatures of the inlet air flow to the combustion turbine.
The interior portions of the hollow body may include a plurality of baffles in spaced-apart relation to thereby define the tortuous path of air flow. The plurality of baffles may be arranged on alternating sides of opposing interior surface portions of the hollow body. For example, the plurality of baffles also may extend inwardly in an interdigitated fashion so that, accordingly, the tortuous path has a serpentine shape.
The hollow body may comprise a tube having an inlet at a first end and an outlet at a medial portion. Additionally, the plurality of baffles may be between the inlet and the outlet. The temperature sensing device may be mounted at a second end of the tube. The tube may have an arcuate first end so that the tube has a J-shape. The inlet of the tube may also be larger than the outlet.
Various types of temperature sensing devices may be carried by the hollow body. For example, the temperature sensing device may be a resistance temperature detector.
An additional aspect of the invention relates to method for sensing inlet air flow temperature for an evaporatively cooled combustion turbine. The method may include connecting a hollow body of an inlet air flow temperature sensor in fluid communication with the inlet air flow, the hollow body carrying a temperature sensing device. The method also may include generating a tortuous path of air flow through an interior of the hollow body to reduce water accumulation on the temperature sensing device, and reading a signal from the temperature sensing device.